This invention relates to aqueous fuel compositions and more particularly, to aqueous fuel compositions whose ingredients are combined in relative proportion so as to achieve a final fuel formulation having a somewhat constant heating value regardless of the hydrocarbon used and the amount and type of alcohol selected. Aqueous fuel emulsion compositions are desirable for use in internal combustion engines because when combusted they produce reduced levels of nitrogen oxide (NOx) emissions.
One problem with using diesel-fueled engines is to the relatively high flame temperatures reached during combustion. Such high temperatures increase the tendency for the production of nitrogen oxides (NOx). These are formed from both the combination of nitrogen and oxygen in the combustion chamber and from the oxidation of organic nitrogen species in the fuel. Nitrogen oxides comprise a major irritant in smog and are believed to contribute to tropospheric ozone, which is a known threat to health. Environmental considerations and government regulations have increased the need to reduce NOx production. Various methods for reducing NOx production include the use of catalytic converters, engine timing changes, exhaust recirculation, and the burning of xe2x80x9ccleanxe2x80x9d fuels. These methods are generally too expensive and/or too complicated to be placed in widespread use.
The rates at which NOx are formed are related to the flame temperature. It has been shown that a small reduction in flame temperature can result in a large reduction in the production of nitrogen oxides. One approach to lowering the flame temperature is to inject water in the combustion zone, however; this requires costly and complicated changes in engine design. The latest attempt to use water to reduce flame temperature is the use of aqueous fuels, i.e., incorporating both water and fuel into an emulsion.
There are various ingredients typically used to make a fuel emulsion including a hydrocarbon, water, alcohol, surfactants, and other additives. Some of these ingredients have a net heat of combustion or lower heating value which means the lower heating value of the final fuel changes based on the amount and type of ingredients selected. Engine manufacturers, however, typically size the engine fuel system based on the heating value per gallon of fuel and cannot tolerate significant variations in final fuel formulations. Thus many aqueous fuel emulsions are formulated with very specific recipes and do not allow for fuel ingredient variability.
For a number of reasons, it would be desirable to develop an aqueous fuel emulsion that can incorporate a wide variety of hydrocarbon sources and can tolerate varying amounts and types of alcohols. For example, alcohols are often used to prevent the aqueous fuel emulsion from freezing at lower ambient temperatures. However, the use of alcohols should be minimized for cost and engine ignition quality considerations. Clearly, there are some engine operating conditions that would warrant increasing the alcohol content of the fuel formulation notwith-standing the extra cost. Similarly, there are some engine operating considerations that would warrant using various hydrocarbon sources, based on the hydrocarbon availability and cost. Thus, it is apparent that there are various engine operating conditions that would benefit from variations in aqueous fuel emulsion formulations.
In general, the invention features a method of formulating a substantially ashless fuel composition that includes: (a) hydrocarbon petroleum. distillate; (b) purified water; (c) alcohols; and (d) an additive package composition comprising various ingredients where a single ingredient may perform multiple functions. The fuel composition preferably is in the form of an aqueous fuel emulsion that is stable at temperatures and pressures encountered during recirculation in a compression ignited engine. The fuel emulsion can be either water continuous emulsion or more preferably a fuel continuous emulsion. More importantly, the aqueous fuel composition can be tailored for specific engine operating conditions by varying the types and amounts of hydrocarbon petroleum distillate and alcohol used while maintaining said aqueous fuel composition within a specified range of acceptable lower heat value.
In preferred embodiments, the fuel emulsion composition includes a hydrocarbon petroleum distillate, purified water, alcohol, and an additive composition that includes an emulsifier and may include other additives such as cetane improvers, surfactants, corrosion inhibitors, lubricity additives, biocides, and antifoam agents.
In the fuel continuous embodiment, the amount of the hydrocarbon petroleum distillate preferably is between about 60 weight percent and about 95 weight percent of the fuel composition, more preferably between about 70 weight percent and about 90 weight percent of the fuel composition.
The purified water preferably contains no greater than about 50 parts per million calcium and magnesium ions, and no greater than about 20 parts per million silicon. More preferably, the purified water contains no greater than about 2 parts per million calcium and magnesium ions, and no greater than about 1 part per million silicon. The amount of purified water preferably is between about 5 weight percent and about 40 weight percent of the fuel composition, more preferably between about 10 weight percent and about 30 weight percent of the fuel composition.
In the water continuous emulsion, the emulsifier preferably is selected from the group consisting of nonionic, anionic, and amphoteric emulsifiers, and combinations thereof. An example of a preferred alkyl amphoteric emulsifier for such water continuous fuel emulsion embodiment is one having at least 12 carbon atoms. A specific example is dihydroxyethyl tallow glycinate. The amount of the alkyl amphoteric emulsifier preferably is between about 0.01 weight percent and about 0.1 weight percent of the fuel composition.
In addition, the water continuous fuel emulsion embodiments includes an alkylphenolethoxylate (e.g., a polyethoxylated nonylphenol having between about 8 and 12 moles of ethylene oxide per mole of nonylphenol, more preferably about 9 moles of ethylene oxide per mole of nonylphenol), an alcohol ethoxylate, a fatty alcohol ethoxylate, an alkyl amine ethoxylate, or a combination thereof within the additive package. In the case of alkylphenol-ethoxylates, the ingredient preferably is present in an amount ranging from about 0.4 weight percent to about 1.0 weight percent of the fuel composition.
The water continuous fuel emulsion embodiment additive composition also may include an organophosphoric or carboxylic mono-, di-, or tri-functional acid having at least 12 carbon atoms. An example of a preferred acid is selected from the group consisting of di- and tri-acids of the Diels-Alder adducts of unsaturated fatty acids (preferably having between about 12 and about 22 carbon atoms) and mixtures thereof. For example, the acid may be a C21 dicarboxylic acid derived from the Diels-Alder adduct of maleic anhydride and oleic acid. The amount of the mono-, di-, or tri-acid preferably is between about 0.04 weight percent and about 0.1 weight percent of the fuel composition, more preferably between about 0.04 weight percent and about 0.05 weight percent of the fuel composition.
The water continuous fuel emulsion additive composition also includes an alkanolamine. Examples of preferred alkanolamines include those selected from the group consisting of amino methyl propanol, triethanolamine, diethanolamine, and combinations thereof, with amino methyl propanol being preferred. The amount of the alkanolamine preferably is between about 0.05 weight percent and about 0.4 weight percent of the fuel composition, more preferably about 0.06 weight percent of the fuel composition.
The water continuous fuel emulsion additive composition further includes an aminoalkanoic acid. An example of a preferred aminoalkanoic acid is available from the Keil Chemical Division of Ferro Corporation under the trade designation xe2x80x9cSynkad 828xe2x80x9d. The amount of aminoalkanoic acid preferably is between about 0.03 weight percent and 0.15 weight percent, more preferably between about 0.03 and about 0.05 weight percent.
The fuel continuous fuel emulsion additive package is comprised of a primary surfactant in combination with one or more surfactant stabilizers and enhancers. Preferred fuel continuous compositions include about 0.3% to about 1.0% by weight, preferably about 0.4% to about 0.6% total additive package.
The primary surfactants in the fuel continuous emulsions include charged amide surfactants, more preferably unsubstituted, mono- or di-substituted amides of saturated or unsaturated C12-C22 fatty acids. The primary surfactant in the fuel continuous emulsion composition is present in the range of about 3,000 ppm to about 10,000 ppm.
The disclosed additive package for the fuel continuous emulsion also includes one or more block-copolymers which act as a stabilizer of the primary surfactant and one or more high molecular weight polymeric dispersants. The disclosed block-copolymers include high molecular weight block copolymers, such as EO/PO block copolymers in the range of about 1,000 ppm to about 5,000 ppm. The disclosed high molecular weight polymeric dispersants are present in the range of about 100 ppm to about 1,000 ppm.
Finally, in some preferred embodiments of both water continuous and fuel continuous emulsions, the additive composition includes antifreeze and ignition delay modifiers (i.e. cetane improvers). The amount of antifreeze preferably is between about 2 weight percent and about 9 weight percent of the fuel composition. Examples of preferred antifreezes include C1 to C3 alcohols, methanol, ethanol and isopropanol. Preferred ignition delay modifiers are selected from the group consisting of nitrates, nitrites, peroxides, and combinations thereof. An example of a preferred ignition delay modifier is 2-ethyihexylnitrate. The amount of the ignition delay modifier preferably is between about 0.1 weight percent and about 0.4 weight percent of the fuel composition.
The components of the fuel emulsion composition, and the relative amounts thereof, are preferably selected such that the fuel emulsion composition is suitable for use in diesel engines. This includes varying the formula of the fuel emulsion to maintain the lower heating value of the fuel emulsion within a range for which the engine fuel system is designed. Moreover, the fuel emulsion composition is preferably ashless, is preferably stable at temperatures and pressures encountered during recirculation in compression ignited engines.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.